Add hint to --time-unit

src/cli.rs

@@ -210,7 +210,9 @@ fn build_command() -> Command<'static> {
                 .takes_value(true)
                 .value_name("UNIT")
                 .possible_values(&["millisecond", "second"])
-                .help("Set the time unit to be used. Possible values: millisecond, second."),
+                .help("Set the time unit to be used. Possible values: millisecond, second.\
+                       This argument affects the command line output as well as AsciiDoc, Markdown and org-mode exports.\
+                       It does not affect JSON and CSV exports."),
         )
         .arg(
             Arg::new("export-asciidoc")